I. Field of the Invention
The present invention generally relates to the field of controls for devices requiring considerable power to operate their controls and, in particular, the present invention is concerned with externally mounted controls for varying the volume of variable volume pumps having an externally projecting control rod that is rotatable to vary the pump displacement or volume.
II. Description of the Prior Art
Variable volume pumps having an externally attached cylinder for varying the pump displacement are known. Control cylinders for controlling variable volume pumps from the exterior of the pump comprise a conventional cylinder with a rod extending from an end thereof with an end of the rod engaging a lever associated with a rotatable control rod projecting from the pump. This type of control cylinder has serious drawbacks such as external leakage from the packing gland around the rod; unequal amounts of oil required to stroke the cylinder in opposed directions; leakage across the control cylinder piston affecting the accuracy and positioning of the control; and an inability of the control cylinder of this type to lend itself to an integrated package design with only a pressure and return line attached to the cylinder. Control devices having a rotary or angular output attachable to the rotatable control rod of a variable volume pump also are known. Devices of this type are also susceptible to malfunction caused by leakage across the cylinder piston, and are susceptible to failure due to leakage past a rotary seal on the output shaft. Examples of rotary operators in the prior art are disclosed in U.S. Pat. Nos. 3,614,913; 3,786,728; 4,094,231; and 4,170,169. These patents are relevant to the applicants' invention in that they represent the closest prior art for utilizing a piston operated by fluid under pressure to produce a rotary motion.
III. Prior Art Statement
The aforementioned prior art, in the opinion of the applicants' and the applicants' attorney, represents the closest prior art of which the applicants' and their attorney are aware.